Edmontonia
Edmontonia (meaning "From the Edmonton Formation") was an armoured dinosaur, a part of the nodosaur family from the Late Cretaceous Period. It is named after the Edmonton Formation (now the Horseshoe Canyon Formation), the unit of rock it was found in. Description Size and general build Edmontonia was bulky and tank-like at roughly 6.6 m (22 ft)1 long and 2 m (6.5 ft) high.needed It had small, ridged bony plates on its back and head and many sharp spikes along its back and tail. The four largest spikes jutted out from the shoulders on each side, two of which were split into subspines in some specimens.1 Its skull had a pear-like shape when viewed from above.1 (Compare 26 feet long and 8 feet high for the M1 Abrams army tank.) Distinguishing traits In 1990, Kenneth Carpenter established some diagnostic traits for the genus as whole, mainly comparing it with its close relative Panoplosaurus. In top view, the snout has more parallel sides. The skull armour has a smooth surface. In the palate, the vomer is keeled. The neural arches and neural spines are shorter than those of Panoplosaurus. The sacrum proper consists of three sacral vertebrae. In the shoulder girdle, the scapula and coracoid are not fused.4 Carpenter also indicated in which way the main species differed from each other. The type species, Edmontonia longiceps, is distinguished from E. rugosidens in lacking sideways projecting osteoderms behind the eye sockets; having tooth rows that are less divergent; possessing a more narrow palate; having a sacrum that is wider than long and more robust; and in having shorter spikes at the sides. Also, an ossified cheek plate, known from E. rugosidens specimens, has not been found with Edmontonia longiceps. Skeleton The skull of Edmontonia, up to half a metre long, is somewhat elongated with a protruding truncated snout. The snout carried a horny upper beak and the front snout bones, the premaxillae, were toothless. The cutting edge of the upper beak continued into the maxillary tooth rows, each containing fourteen to seventeen small teeth. In each dentary of the lower jaws, eighteen to twenty-one teeth were present. In the sides of the snout large depressions were present, "nasal vestibules", that each possessed two smaller openings. The top of these was a horizontal oval and represented the bony external nostril, the entrance to the nasal cavity, the normal air passage. The more rounded second opening below and obliquely in front, was the entrance to a "paranasal" tract, running along the outer side of the nasal cavity, in a somewhat lower position. A study by Matthew Vickaryous in 2006 proved for the first time the presence of multiple openings in a nodosaurid; such structures had already been well established in ankylosaurids. The air tracts are however, much simpler than in the typical ankylosaurid condition, and are not convoluted while lacking bony turbinate bones. The nasal cavity is separated into two halves along the midline by a bone wall. This septum is continued to below by the vomers, which are keeled, the keel featuring a pendulum-shaped appendage.5 Another similarity with Ankylosauridae is the presence of a secondary bone palate, a possible case of parallel evolution. This has been shown too for Panoplosaurus. The head armour tiles, or caputegulae, are smooth. Details differ between the various specimens but all share a large central nasal tile on the snout, bend large "loreal" tiles at the rear snout edges and a large central caputegula on the skull roof. The tiles behind the upper eye socket rim in Edmontonia longiceps do not stick out as much as in E. rugosidens, combined with a more narrow, pointed snout in the former. Some E. rugosidens specimens are known that possess a "cheek plate" above the lower jaw. Contrary to that discovered with Panoplosaurus, it is "free-floating", not fused with the lower jaw bone. E. schlessmani was described as having a wide rear skull.6 The vertebral column contains about eight neck vertebrae, about twelve "free" back vertebrae, a "sacral rod" of four fused rear dorsal vertebrae, three sacral vertebrae, two caudosacrals and at least twenty, but probably about forty, tail vertebrae. In the neck the first two vertebrae, the atlas and axis, are fused. In the shoulder girdle, the coracoid has a rectangular profile, in contrast to the more rounded shape with Panoplosaurus. Two sternal plates are present, connected to sternal ribs. The forelimb is robust but relatively long. In Edmontonia longiceps and E. rugosidens the deltopectoral crest of the humerus is gradually rounded. The metacarpus is robust compared to that of Panoplosaurus. The hand very likely was tetradactyl, having four fingers.4 The exact number of phalanges is unknown but the formula was by W.P. Coombs suggested to be 2-3-3-4-?. Osteoderms Apart from the head armour, the body was covered with osteoderms, skin ossifications. The configuration of the armour of Edmontonia is relatively well known, much of it having been discovered in articulation. The neck and shoulder region was protected by three cervical halfrings, each consisting of fused rounded rectangular, asymmetrically keeled, bone plates. These halfrings did not have a continuous underlying bone band. The first and second halfrings each had three pairs of segments. Below each lower end of the second halfring a side spike was present, a separate triangular osteoderm pointing obliquely forward. In the third halfring over the shoulders, the two pairs of central segments are bordered on each side by a very large forward-pointing spike that is bifurcated, featuring a secondary point above the main one. A third large spike behind it points more sideways; a smaller fourth one, often connected to the third at the base, is directed obliquely to behind. The row of side spikes is continued to the rear but there the osteoderms are much lower, curving strongly to behind, with the point overhanging the rear edge. Gilmore had trouble believing that the shoulder spikes really pointed to the front as this would have greatly hampered the animal while moving through vegetation. He suggested that the points had shifted during the burial of the carcass. However, Carpenter and G.S. Paul, trying to reposition the spikes, found that it was impossible to rotate them without losing conformity with the remainder of the armour. The side spikes have solid, not hollow, bases. The spikes differ in size between E. rugosidens individuals; those of the E. longiceps holotype are relatively small.4 Behind the third halfring the back and hip are covered by numerous transverse rows of much smaller oval keeled osteoderms. These are not ordered in longitudinal rows. The front rows have plates oriented along the length of the body, but to the rear the long axis of these osteoderms gradually rotates sideways, their keels ultimately running transversely. Rosettes are lacking. The configuration of the tail armour is unknown. The larger plates of all body parts were connected by small ossicles.4 Such small round scutes also covered the throat. Discovery and species In 1915, the American Museum of Natural History obtained the nearly complete, articulated front half of an armoured dinosaur. In 1922, William Diller Matthew referred this specimen to Palaeoscincus.2 In 1940, Lori Russell referred it to Edmontonia rugosidens.3 The type species of Edmontonia, E. longiceps was discovered in 1924 by George Paterson. It wasn't named until 1928 by C. M. Sternberg. E. rugosidens, formally named by Gilmore in 1930, is reported from the Aguja formation in Texas. Edmontonia species include: ##''E. longiceps'', the type, is known from the middle Horseshoe Canyon Formation (Unit 2) dated to 71.5-71 million years ago.4 ##''E. rugosidens'', is sometimes given its own genus, Chassternbergia, first coined as a subgenus by Dr. Robert T. Bakker in 1988 (Edmontonia (Chassternbergia) rugosidens) and based on differences in skull proportion from E. longiceps and its earlier time period.56 This subgenus or genus is not generally accepted;78 It is found in the lower Dinosaur Park Formation, dating about 76.5-75 million years ago.4 ##And E. australis,6 which is known from cervical scutes only, and is considered to be a dubious name7 or a synonym of Glyptodontopelta mimus.9 Usually included in this genus is Denversaurus schlessmani ("Schlessman's Denver lizard"). This taxon was erected by Bakker in 1988 for a skull from the Late Maastrichtian Upper Cretaceous Lance Formation of South Dakota,5 but considered by later workers to belong to Edmontonia rugosidens.8 The type specimen of Denversaurus is in the collections of the Denver Museum of Natural History (now the Denver Museum of Nature and Science), Denver, Colorado (for which the genus was named). Phylogeny Paleobiology Category:Nodosaurs Category:Dinosaurs of North America Category:Cretaceous dinosaurs